[ https://issues.apache.org/jira/browse/HIVE-584?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Ning Zhang reassigned HIVE-584:
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Assignee: (was: Ning Zhang)
> Clean up global and ThreadLocal variables in Hive
> -------------------------------------------------
>
> Key: HIVE-584
> URL: https://issues.apache.org/jira/browse/HIVE-584
> Project: Hadoop Hive
> Issue Type: Improvement
> Affects Versions: 0.3.0, 0.3.1
> Reporter: Zheng Shao
>
> Currently in Hive code there are several global and ThreadLocal variables that need to
be cleaned.
> Specifically, the following classes are involved:
> 1. HiveConf: contains hive configurations (and a classloader)
> 2. Hive class: contains a static member Hive db. Hive class contains a member HiveConf
conf, as well as a ThreadLocal storage of IMetaStoreClient.
> 3. SessionState: contains a static ThreadLocal storage of SessionState. SessionState
class contains a Hive db, a HiveConf conf, a history logger, and a bunch of standard input/output
streams
> 4. CliSessionState: SessionState plus some command options and the command file name.
> 5. All classes that try to get Hive db or HiveConf from global static Hive db, or SessionState.
> There are several problems with the current design. To name a few:
> 1. SessionState instances are ThreadLocal, but SessionState contains Hive db which also
contains ThreadLocal storage. Not sure a db can be shared across different threads or not?
What is the global static Hive db?
> 2. We pass HiveConf and Hive db in two ways to classes like Task: Sometimes through initialize(),
sometimes through SessionState. This complicates the code a lot. It's hard to know which HiveConf
and which db we should use.
> We need to think about a better way to do it.
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